Mr Mustang-then please explain the following:

The following carbs came from the factory:
MOPAR 340-625cfm
MOPAR 340-1050CFM
MOPAR 440-1350 CFM
426 HEMI-1200 CFM
455SD & 455HO-850cfm
454Chevy-850cfm
455Olds-850cfm
__________________________________________________ __

Joe,a return line is typically a 4AN line(on a carbed motor)that returns fuel to the tank.This does two things:
1-it keeps the pump from "deadheading"
2-it keeps fuel cooler by circulation

I would have placed the P-guage at the end of the run also.In fact,my guage is at the end of the fuel rail on my car(FI motor).

Again,there are two common ways of plumbing this set-up:
1- is to use a regulator to return fuel to the tank.
2-a fitting can be tapped to except a Holley jet of the appropriate size to regulate the returning fuel.

CobraBill

If the pump "deadheads" would you hear a difference in the sound of the fuel pump? Would the pitch/sound change?

Joe

Bill,

You keep forgetting that those engines were burning a different level and octane rating fuel source. The same engine today, with just a set of hardened valve seats to run modern fuel will run better with a small carb than the original carbs that they came with. Again I'm not saying these things just to see myself post, I'm telling you what the last 5 years of real world experience with a computerized chassis dyno that compensates for day to day weather changes and air fuel ratios has taught me. If you want to continue on with the old school way of thinking without giving a new idea a try, then you are the one who is no longer open to a better way of doing things. My case in point will be a 351W/385HP Ford crate engine, which started life with a 750cfm Holley Carb that both Ford Motorsports and Holley suggested, then went through a set of Holley street avengers of the 670 and 770 variety, another Holley 650cfm dp and ended up with a 600cfm dp in the end. The 600cfm DP not only produced the cleanest runs across the spectrum (part throttle, full throttle, and throttle response from 570 rpms (idle) to 6,200rpms (where I chickened out), but made more than 22hp and 28ft/lbs of torque more than any of the other carbs (all tuned to the best they could be)........These are not numbers at the flywheel, but at the rear wheels after going through the entire drivetrain and their inherent loads........Now, back to your examples posted below, taking into account that these engines were set up on an engine dyno and tweaked for full throttle performance and not partial throttle performance, again, which would you choose now knowing that they could not even think to take into account the real world drivetrain loads when they decided on which carbs to plunk down on a particular engine back in the 60's?


Bill S.

PS: You want to give me unlimited funds and a car with each of those engines listed below in stock (+ hardend valve seats for modern fuel) form, I'll be more than happy to rent the local chassis dyno and prove my point for you up close and personal.......

PSS: The other example would be the 427 Sideoiler in my last ERA Cobra, when I bought it it had a 850cfm Holley carb on it that the original engine builder set up. When I switched it to a 650CFM carb, I made almost 41 more HP and 62ft/lbs of torque when on the chassis dyno. Throttle response was crisper and cleaner, and the engine just wanted to scream past redline.........Where the original carb, even after two hours of tuning time (at $150/hr) on the dyno, still ran terrible....

How about something simple. Is the gas cap venting? I had to modify mine by grinding a little slot in the metal part of the locking gas cap.

I don't think that is the issue..Keep in mind the car runs fine at freeway speeds and before it is fully warmed up. That is why I am leaning towards the hot fuel conclusion as the main issue. The only other question is why does it seem to first happen when coming off of load, slowing down for a stop light, etc.

I think Mr.Mustang makes some good points as well.

Joe

Just a thought!!! I was having similar problems,I changed from a manual pump to electric, took the carb apart a few times. It turned out that my distributor was worn and shorting out,backfiring etc. Bought a new distributor,Hey Presto.
Check it just to eliminate.

Just got off the phone with the shop and they think the problem is that fuel in the lines is getting too hot. My regulator is most likely a deadhead type regulator so I am thinking switching to a return type regulator may take care of this. Thoughts?

Joe

I think I suggested that about 15 or so posts ago..

I don't think it's a carb problem. Your symtoms duplicate mine before I went to a return fuel system. With a single fuel line you're prone to pressure creep during low fuel demand. You might look at your fuel gauge and only see 6 psi.. What pressures aren't you seeing with the hood shut? Warmer temps will also aggravate the problem causing flooding more often.

Joe-do the return line.I don't buy the "hot fuel line" thing.Sounds like they are grabbing for straws.%/ As for the sound,you'll hear it with the engine off.A combination of the pump & underhood temps COULD be causing a spike that pushes the needle off the seat.



MR Mustang-i can see your point.To a point.

PSSSSSSSS-my side-oiler(17 over) has a Braswell carb that started life as an 850CFM and is now just shy of 1000cfm.Absolutely flawless and returns about 17 mpg on a trip.( not that i give a rats ass about fuel milage,but an indicator of it's effeciency)
www.braswell.com

I just came back from the shop and we are going to install a bypass regulator with the return. When I was there he showed by at least 5 different places where, even in my un-educated opinion, was way too close/up against heat sources. So we will also be doing some re-routing. So while I don't think it was "THE" cause, I certainly think it was contributing to it.

Joe

COOL!(pun intended)Let us know what happens.